In the manufacture of transparent containers such as glass bottles, various types of checks or defects may occur in the sidewalls, heels, bottoms, shoulders and/or necks of the containers. These checks or defects, termed "commercial variations" in the art, can affect commercial acceptability of the containers. The commercial variations may be opaque, such as stones, or may be refractive such as blisters, bubbles or tears.
It has heretofore been proposed to employ electrooptical inspection techniques for detecting commercial variations that affect optical properties of the containers. The basic principle is that a light source is positioned on one side of the container and a camera is positioned on the other. The light source may be configured to have an intensity that varies across one dimension of the source. Light rays normally travel from the source straight through the container and focused onto the camera, and are viewed at the camera at a given intensity. However, a refractive commercial variation bends the light ray as it travels through the container sidewall, so that the image projected onto the camera is of a different area of the light source. If such different area has a different intensity than the area normally imaged onto the camera, the camera can detect the refractive sidewall defect.
U.S. Pat. No. 4,610,542 discloses one technique for varying the effective intensity of the light source across the light source. An elongated filament lamp is positioned along the upper edge of a diffuser plate to produce an intensity gradient in the vertical direction across the light source. The upper area of the diffuser plate is brightest, the middle area has average brightness and the lower area is darkest. U.S. Pat. No. 4,601,395 discloses another technique in which a filter is placed across the light source diffuser screen to provide differing areas of effective light source intensity.
Although the systems disclosed in the noted patents, both of which are assigned to the assignee hereof, address problems theretofore extant in the art, further improvements remain desirable. In particular, container inspection systems of the character disclosed in the noted patents typically include a starwheel conveyor for conveying containers to and through the inspection station, and for holding the container stationary while it is rotated about its axis during the inspection process. The light source is positioned within the arcuate conveyor path --i.e., within the diameter of the starwheel--which creates space problems and necessitates use of a fairly large starwheel. Another difficulty with typical inspection systems heretofore proposed lies in the difficulty in detecting sharp-edged defects such as ribbon tears.
It is therefore a general object of the present invention to provide an inspection apparatus and method in which the major optical components--i.e., the light source and camera --are disposed on one side of the conveyor path, preferably externally of the arcuate path of a starwheel conveyor, which therefore forms a more simple and compact inspection system, and permits use of a smaller starwheel with reduced inertial and energy consumption. Another object of the present invention is to provide an apparatus and method for inspecting transparent containers of the described type that provide enhanced detection of sharp-edge commercial variations such as ribbon tears, as well as detection of other typical commercial variations such as stones, blisters, bubbles, lap marks and blowouts.